Muscles  Muscle: organ that can relax, contract, and provide the force to move your body parts  Energy is used and work is done  More than 600 muscles in the body

Can you think of an activity you do that doesn’t require muscles?

 No! As long as you are alive, your muscles are still moving Digestive system, beating heart, and breathing all require moving muscles

Muscles are divided into 2 main categories – can you name them?

Voluntary muscles  Muscles you are able to control  Used when you lift your leg, move your pencil, raise your hand, etc.

Involuntary muscles  Muscles you can’t control consciously  Control activities such as pumping blood through blood vessels and moving food through digestive system

Muscle tissue  Muscles are made of tissue  There are 3 types: can you name them?

Skeletal muscle  Muscles that move bones  Most common muscle type  Attached to bone by tendons: thick bands of tissue  Look striped/striated when you look at them under a microscope  Contract quickly and tire more easily  Are skeletal muscles voluntary or involuntary?

 Voluntary

Skeletal muscle

Smooth muscle  Found in intestines, bladder, blood vessels, and other internal organs  Not striated (striped)  Involuntary  Slowly contract and relax, do not tire easily

Smooth muscle

Cardiac muscle  Makes up the walls of the heart  Striated like skeletal muscle  Involuntary like smooth muscle  Contracts about 70 times per minute

Cardiac muscle

How muscles work  Always pull, never push  Often work in pairs (one contracts while the other relaxes)  Can become larger or smaller over time depending on how they are used  Need energy to contract and relax Contracting muscles release mechanical energy (movement) and thermal energy (heat)

Assignment – pick one!  Write a poem comparing and contrasting the three types of muscle  Draw a picture of the human body’s muscular system. Label 2 places where you can find each of the 3 muscle types and explain how you know you can find them there  Use clay to make a model of each muscle type. Your models must clearly show the identifying features of that type of muscle  Due Friday, 2/11

What is the largest organ (not solid) in the human body?

What are the 3 layers of the skin?

Epidermis  Outer, thinnest layer  Outermost cells are dead and water repellent  Cells rub off constantly

Dermis  Middle layer  Contains blood vessels, nerves, muscles, sweat glands

Fatty layer  Innermost layer  Insulates the body

What is melanin?

Melanin  Pigment that protects skin and gives it color  Lighter skin tones mean you have less melanin  Less melanin means less protection from sun’s rays

What does skin do for your body?

Main functions of the skin  Vitamin D formation  Heat and waste exchange  Protection  Rids body of waste  Sensory response

Bruises  Blood vessels under skin burst  Blood cells release hemoglobin, which breaks down into pigments  Pigments cause skin to change color  Bruise turns yellow as pigment breaks down and reenters bloodstream

Cuts  Cut: any tear in the skin  Blood flows until clot forms  Scab covers opening to prevent bacteria from entering body  Scar: thick tissue that forms to fill opening

Skin grafts  Pieces of skin that are cut from one part of a person’s body and moved to another area  Used for bad injuries or burns  Must be taken from victim’s own body or an identical twin to be successful Skin transplants from cadavers or other sources will typically be rejected in a few weeks

Assignment – pick one!  Pretend that you are skin, and you have just gotten a bruise or cut. Write a story (as the skin) explaining what has happened, including the healing process you must go through.  Draw a diagram that shows how skin may get injured and how it repairs itself.  Interview a skin cell, asking it to explain how it functions, the hard times in its life, and how it overcomes them.  Due Monday, 3/7